Method for extending a nozzle and extended nozzle for rocket drives

ABSTRACT

A method for extending a nozzle for a rocket engine is described, in which at least one second region of the contour of the nozzle is arranged as an extension of a first region of the contour of the nozzle. This extension of the first region by the second region occurs at an altitude at which the contour of the open jet of the rocket engine substantially corresponds to the contour of the second region. Also described is a corresponding extendible nozzle for a rocket engine.

This application claims the benefit of priority of German patentdocument number 101 23 731.6, filed May 15, 2001, the disclosure ofwhich is expressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a method for extending a nozzle for arocket engine and to an extendible nozzle for a rocket engine.

Rocket engines used today typically have nozzles with a continuousnozzle contour, so-called bell nozzles. The power of these engines,however, during the ascent of the corresponding missile or spacecraft,is limited at higher altitudes because of the defined nozzle contour. Anideal “altitude compensating” nozzle would adapt the area ratio and thusthe nozzle contour to the corresponding altitude during the ascent insuch a way that the average nozzle pressure in the exit nozzle at thenozzle end would always match the ambient pressure (“compensated”nozzle). The average nozzle pressure used for this purpose is obtainedby one-dimensional or two-dimensional averaging of the pressure acrossthe nozzle cross-section of the propellants ejected through the nozzle.This would result in a full-flow nozzle with a continuously optimalspecific pulse during the ascent. For technical reasons, however, it hasnot thus far been possible to realize this.

Based on their fixed nozzle geometry, conventional engines achieve theiroptimal power only at a certain point of the flight trajectory. Belowthat point, the nozzle flow is overexpanded (at low altitude the ambientpressure is greater than the average pressure at the end of the nozzleof the propellants ejected through the nozzle). Above the optimal point,the flow is underexpanded (the ambient pressure is lower than theaverage pressure at the end of the nozzle of the propellants ejectedthrough the nozzle). After leaving the nozzle, the propellants ejectedfrom the nozzle form a so-called open jet, which depending on thepressure ratios can be constricted or expanded compared to the nozzleend cross section. This is also illustrated in FIGS. 1 and 2. For thisreason, engines equipped with such nozzles require a compromise betweenthe engine output at sea level and the engine output at higher altitudesto maximize the payload for a given mission, particularly in the vacuumof space in the case of spacecraft engines. These problems arediscussed, for example, in U.S. Pat. No. 3,394,549 and in J. E. Beck andM. D. Horn, “Altitude Compensating Nozzles,” Rockwell Threshold, Summer1995, pp. 38 to 44.

The engine output is further limited by the requirement of a full-flownozzle at sea level to prevent side loads (lateral force effects) on thenozzle contour. In conventional bell nozzles these lateral forces occurwhenever the flow near the wall of the propellants ejected by the nozzleis separated from the nozzle contour starting from the nozzle endbecause the ambient pressure is too high and air from the environmentflows into the nozzle. Because of the turbulent and thus unsteadybehavior of the flow field in this region, lateral forces occur despitea perfectly axisymmetric configuration of the nozzle contour, of theinflow within the nozzle of the propellants to be ejected through thenozzle and of the environmental conditions. Additional lateral forcesare caused if the conditions do not meet the ideal axisymmetric case. Toprevent these side-loads on the ground and during the first phase of theascent of the missile or spacecraft, all the existing engines require aso-called full-flow nozzle on the ground. The wall pressure at the endof the nozzle must be sufficiently high to prevent the flow fromseparating from the nozzle contour. As a result, however, the maximumallowable area ratio and thus the engine output at higher altitudes,particularly in a vacuum if the rocket engine is used for a spacecraft,are limited.

The vacuum power of first-stage engines with bell nozzles can beincreased by using nozzles with controlled flow separation, which makesit possible to realize a greater area ratio. A concept for “altitudecompensation” of the nozzles is realizable through controlled flowseparation in the nozzle. The side loads and the thrust loss can bereduced through overexpansion at low altitudes during the first part ofthe flight trajectory.

These concepts use different techniques for generating as symmetrical aflow separation as possible. Such methods include, for example, theactive axisymmetric injection of secondary gases or the passiveaxisymmetric ventilation of the nozzle with ambient air. The flow canalso be actively caused to separate by mounting additional components,such as tripwires, ablating inserts or a diffuser at the nozzle exit,which is discarded during the flight. Such proposals are described, forexample, in R. H. Schmucker, “Side loads and their reduction in liquidrocket engines,” Report TB-14, 24th International AstronauticalCongress, Baku, USSR. Oct. 7 to 13, 1973.

Other prior art concepts achieve a flow-controlling separation purelythrough the contour design with an invariable structure of the nozzlecontour without any movable parts. This includes the so-called dual bellnozzle concept as well as a polygonal nozzle concept.

In the dual bell nozzle, a controlled separation is achieved through adiscontinuous nozzle contour, i.e., a sharp bend in the contour. Suchnozzles are disclosed, for example, in the initially cited U.S. Pat. No.3,394,549 and in J. E. Beck and M. D. Horn, “Altitude CompensatingNozzles,” Rockwell Threshold, Summer 1995, pp. 38 to 44. Here, thenozzle has a first region with a first contour and a second region witha second contour adjoining the first. During the ascent of the boosterrocket, the sharp bend in the contour produces two different states ofthe flow of the propellants ejected through the nozzle. In the groundmode (low altitude and high ambient pressure) the flow is in contactwith the nozzle contour only in the first region. The flow symmetricallyseparates at the sharp bend in the contour (i.e., at the end of thefirst region) and completely separates downstream thereof (i.e., in thesecond region). In other words, an open jet forms in the second region.The controlled and symmetrical flow separation at the sharp bend of thecontour reduces the side loads at low altitudes. As the missile or thespacecraft ascends, the decreasing ambient pressure drops below acritical value at a certain altitude, and the flow is in contact withthe wall in the second region as well. As a result, starting from thisaltitude, the flow is in full contact with the nozzle contour throughoutthe entire nozzle.

The concept of the polygonal nozzle is described, for example, in WO97/29277. In this concept, starting from a certain area ratio, a contourwith a polygonal cross-sectional area (approximately 5 to 7 edges) isused. This is intended flow-dynamically to decouple the individualsegments through the different expansion of the propellant gases fromthe corners to the edge centers in order to reduce the wall pressurecorrelations in circumferential direction and the aerodynamic sideloads. It is further intended to reduce the susceptibility toaeroelastic coupling between separation and mechanical vibrations.

The dual bell concept and the polygonal concept have the advantage ofbeing structurally simple because they require no additional mechanicalor moving parts. A drawback of these nozzle designs, however, is thegreat length of such nozzle structures. Depending on certainconfigurations of the corresponding missile or spacecraft, this may leadto conflicts with the allowable mounting dimensions. Furthermore, if thestructural area is large, the great overall length is sensitive topressure pulsations (buffeting), which are caused by the external flowand which can cause high lateral mechanical loads on the shell or on theinner wall of the nozzle in the region of the separated flow.

A means to realize high area ratios at high altitudes, particularly in avacuum, are the so-called extendible nozzles. The nozzle contour as arule consists of two parts: the lower downstream part is extended ordeployed at high altitude and is coupled to the end of the upper part.Such extendible nozzles are described for example in U.S. Pat. No.4,947,644, U.S. Pat. No. 4,383,407 and in J. E. Beck and M. D. Horn,“Altitude Compensating Nozzles,” Rockwell Threshold, Summer 1995, pp. 38to 44. Specifically, U.S. Pat. No. 4,947,644 describes a nozzlestructure in which a discontinuous nozzle contour is produced bydeploying individual elements. The problem, however, is that when thenozzle contour is extended in this manner, high side loads and heatloads may occur during the extension process on the portion of thenozzle contour that is to be extended or deployed if the nozzle contourgets into the area of the open jet of the engine. This is particularlyproblematic in the technical concept of U.S. Pat. No. 4,947,644.

Thus, the object of the present invention is to provide a means toimprove the adaptation of a rocket engine nozzle to different altitudeswhile minimizing the loads on the nozzle structure.

In one embodiment of the inventions there is a method for extending anozzle for a rocket engine, in which at least one second region of thenozzle contour is arranged as an extension of a first region of thenozzle contour. In other words a so-called extendible nozzle isprovided. This extension of the first region by the second region occursat an altitude at which the contour of the open jet of the rocket enginesubstantially corresponds to the contour of the second region. In thisinvention, the second region, therefore, does not have just anystructure, but a structure that substantially corresponds to the contourof the open jet at the specified altitude. This essentially means thatthe contour of the second region does not necessarily have to exactlymatch the contour of the open jet. Rather, interaction effects (e.g.,the ejector effect) that occur during the extension of the nozzle if thesecond region is arranged in the area of the open jet can also be takeninto account when the contour is determined. This contour can bedefined, e.g., using tests or simulations. Adapting the contour of theat least one second region to the contour of the open jet and carryingout the extension process of the nozzle during that portion of theflight trajectory in which the contour of the at least one second regionsubstantially matches that of the open jet makes it possible to clearlyreduce the occurring loads, particularly side loads and heat loads. Theextension of the nozzle contour at a defined altitude contributes to theadjustment of the nozzle to the conditions at higher altitudes and thusenables a more effective use of the rocket engine. During the firstflight segment from the ground up to the defined altitude, no flowseparation occurs in the first region of the nozzle contour, and therocket engine operates with a relatively low area ratio. Aftercompletion of the first flight segment, the nozzle is extended by the atleast one second region to operate at a greater area ratio and thus toimprove the performance at a higher altitude, possibly in a vacuum.

The special contour of the at least one second region depends on thealtitude at which the nozzle is extended. For example, the extension ofthe first region preferably occurs at an altitude where the ambientpressure is lower than the average nozzle pressure of the propellantsbeing ejected through the nozzle at the end of the first region. Theaverage nozzle pressure is obtained by one-dimensional ortwo-dimensional averaging of the pressure across the nozzlecross-section of the propellants ejected through the nozzle. This meansthat the first flight segment is carried out at a slight overexpansion(on the ground) or a slight underexpansion (at the end of the firstflight segment), such that the contour of the at least one second regionis expanded compared to the first region. In principle, however, it ispossible to provide a different contour that corresponds to theconditions at a different altitude.

In principle, the nozzle can be extended by different extensionmechanisms, e.g., by folding it out or swinging it out. Preferably, thesecond region is extended in longitudinal direction of the nozzle, sinceprecisely this makes it possible to guarantee a defined movement of theat least one second region relative to the first region whilesimultaneously maximizing mechanical stability. Until the end of theextension process, the at least one second region practically does notengage with the area of the open jet. This, in turn, reduces the loadsacting on the nozzle.

The present invention further comprises an extendible nozzle for arocket engine in which the nozzle contour in longitudinal direction ofthe nozzle has a first region with a first contour and at least onesecond region with a second contour. The at least one second region isconfigured to extend the first region while forming a discontinuousnozzle contour.

The contour of the at least one second region is adapted to the contourof the open jet at an altitude at which the ambient pressure is lowerthan the nozzle pressure of the propellants being ejected through thenozzle. The at least one second region is configured to be extendible inlongitudinal direction of the nozzle. Conventional mechanisms, e.g.,those disclosed in U.S. Pat. No. 4,383,407, can be used as the extensionmechanisms.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a section of the nozzle contour of arocket engine at low altitudes with overexpansion of the propellantsbeing ejected through the nozzle,

FIG. 2 is a schematic view of the section shown in FIG. 1 but at highaltitudes with underexpansion of the propellants being ejected throughthe nozzle, and

FIG. 3 is a schematic view of the extension of the nozzle according toan embodiment of the invention by extending a second contour region atan altitude with underexpansion.

DETAILED DESCRIPTION

The concept of an extendible nozzle for a rocket engine in which thenozzle has a first fixed contour region and a second extendible contourregion will now be described. Such a concept is applicable, inparticular, for use in a lower stage engine of a spacecraft, such as abooster rocket. In principle, the engine could be shut off during theextension process, but this would require restarting the engine, whichis connected with an increased risk of failure, and would necessitate anincreased development and qualification effort. In addition, there wouldbe a coasting phase of the booster, which could cause a non-optimizedflight trajectory. It is therefore desirable to extend the secondcontour region of the nozzle while the engine is operating. Criticalduring the extension process is especially the interaction between theopen jet of the engine and the extendible nozzle. Particularly importantin the context of the extension process are the mechanical and thermalloads during contact of the open jet with the wall of the second region.Until now, these loads could be absorbed only by a complex design of theentire engine, which undesirably increases the weight of the engine.

FIGS. 1 and 2 schematically illustrate the behavior of the open jet of arocket engine at different altitudes. The figures each show one half ofthe first region 1 of the nozzle contour of the rocket engine in crosssection. This first region 1 is fixed to the remaining rocket engine andhas a bell-shaped contour. Each of the figures further shows the openjet 2, i.e., the boundary of the contour of the open jet of the rocketengine.

FIG. 1 illustrates the ratio at a low altitude H0, e.g., on the ground.Here, overexpansion is present, i.e., the average nozzle pressure Pm,eof the propellants ejected through the nozzle in the exit plane at theend of the first region is lower than the ambient pressure PaPm,e<PaFor this reason, the edge of the open jet 2 proceeds within theextension of the contour of the first region 1 of the nozzle contour.The average nozzle pressure results, for example, from a two-dimensionalaveraging of the nozzle pressure in the exit plane. Furthermore, withinthe open jet, a pressure adaptation results from a compression shock 3,which is depicted schematically in FIG. 1.

FIG. 2 illustrates the behavior at an altitude H1, for example in thevacuum of space. Here, an underexpansion is present, i.e.,Pm,e>PaIn this case, the pressure adaptation occurs through an expansion of thepropellants ejected through the nozzle, i.e., the open jet fans out,which is schematically illustrated as an expansion fan 4. The edge ofthe open jet now proceeds outside the extension of the contour of thefirst nozzle region 1.

FIG. 3 shows the deployment of a nozzle extension according to theinvention in the form of a second region 5, which in a longitudinaldisplacement indicated by an arrow is shifted to the end of the firstregion 1.

If a nozzle extension as depicted in FIG. 3 were to be deployed at analtitude H0, the open jet would contact the wall of the second region 5as a result of what is called an ejector effect. This would cause highside loads, however, because this contact would be connected with anabrupt expansion of the open jet. An uncontrolled flow separation fromthe wall of the second region 5 could subsequently also occur, which inturn would lead to correspondingly high loads on the engine.Furthermore, after the extension of the second region at this altitudeunder constant operational conditions of the engine, additionalresistance would initially be produced because the ambient pressurewould be higher than the nozzle pressure in the second region 5.

However, the second region 5 that serves to extend the nozzle canproduce additional thrust immediately after completion of the extensionif this second region 5 is extended at an altitude H1 because in thatcase it is possible to realize a nozzle contour with a nozzle pressuregreater than the ambient pressure. If conventional contouring of theextended nozzle with a continuous curve of the contour at the interfacebetween the first region 1 and the second extendible region 5 wereprovided, the pressure would drop in the second region and the nozzlecontour would by no means correspond to the contour of the edge of theopen jet at this altitude H1 at which an extended nozzle can in effectprovide additional thrust. In such a case, the open jet mustconsequently adapt to the contour of the nozzle. During thisthree-dimensional adaptation process increased side loads occur.Furthermore, the different contours of nozzle and open jet edge causeincreased heat loads during the extension process because the nozzlemust be extended into the edge area of the open jet.

Thus, the idea of the present invention is to design the contour of thesecond extendible region 5 in conformity with the contour of the edge ofthe open jet 2 at the time of the extension, ideally (except forpossibly taking into account interaction effects such as the ejectoreffect) corresponding to the contour of the open jet edge 2 at thecorresponding altitude H1 at which the second region 5 is to beextended, as depicted in FIG. 3. With such a contour of the secondregion 5, the open jet needs to be adapted to the contour only slightlyor, ideally, not at all. Because the contour of the second region 5 isvery similar to the contour of the open jet 2, only very minor sideloads and heat loads occur during the extension process. Slightdeviations between the contour of the nozzle and the contour of the openjet 2 may result because of possible adaptations based on the ejectoreffect during the extension process. The pressure near the open jet isthen reduced compared to the actual ambient pressure as soon as thesecond region 5 interacts with the open jet 2 during the extensionprocess.

In any case, the contour of the nozzle in its extended state, nowconsisting of the first region 1 and the second region 5, has a sharpbend between the two regions because the contour of the second region 5is expanded relative to the contour of the first region 1. This resultsfrom the fact that the open jet, due to the underexpansion in the firstregion 1, expands to the corresponding ambient pressure prior to theextension of the second region. As a consequence, the contour of thesecond region 5—if one neglects the above-described ejector effect—isapproximately the contour of a line with constant pressure, which aftercompletion of the extension then leads to a constant wall pressure alongthe wall of the second region 5. Such a contour can be generated, forexample, using the method of characteristics, which is known per se. Thewall pressure results from an optimization of the launching trajectory.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1. A method for extending a nozzle for a rocket engine, comprising thesteps of: providing a first nozzle portion attached to the rocketengine; providing a second nozzle portion, wherein the contour of secondnozzle portion is arranged to be an extension of the first nozzleportion and to conform to a contour of an open jet from the first nozzleportion at a deployment altitude at which the ambient pressure is lowerthan an average propellant pressure at an exit end of the first nozzleportion; maintaining the second nozzle portion in a stowed positionduring a first period of rocket engine operation; and extending thesecond nozzle portion to a deployed position, wherein an inlet end ofthe second nozzle portion is aligned with the exit end of the firstnozzle portion to form a single extended nozzle, when the deploymentaltitude is reached.
 2. The method of claim 1, wherein the step ofextending the second nozzle portion from the stowed position isaccomplished by at least one of longitudinal displacement, pivoting, andunfolding of the second nozzle portion.
 3. The method of claim 1,wherein the second nozzle portion is formed by a plurality of nozzlesections, and during the extending step, the nozzle sections extend fromstowed positions to deployed positions without passing through the openjet.
 4. An extendible nozzle for a rocket engine, comprising: a firstnozzle portion attached to the rocket engine; and a second nozzleportion, wherein the contour of second nozzle portion is arranged to bean extension of the first nozzle portion and to conform to a contour ofan open jet from the first nozzle portion at a deployment altitude atwhich the ambient pressure is lower than an average propellant pressureat an exit end of the first nozzle portion, wherein the second nozzleportion is extended from a stowed position to a deployed position,wherein an inlet end of the second nozzle portion is aligned with theexit end of the first nozzle portion to form a single extended nozzle,when the deployment altitude is reached.
 5. The extendable nozzle ofclaim 4, wherein the second nozzle portion is adapted to be extendedfrom the stowed position to the deployed position by at least one oflongitudinal displacement, pivoting, and unfolding.
 6. The extendiblenozzle of claim 5, wherein the second nozzle portion is formed by aplurality of nozzle sections, wherein the nozzle sections are adapted tobe extended from stowed positions to deployed positions without passingthrough the open jet.